"EVENT_STOP" and "EVENT_PROPAGATE" are designed for the return from widget event signal handlers and similar, being true to stop or false
to propagate. The names can help you avoid confusion over which way is true and which is false. (You can also remember the return as
meaning "handled", which is the jargon in a few other signal handler types.)
Gtk2::EVENT_STOP # true
Gtk2::EVENT_PROPAGATE # false